1. Field of the Invention
This invention relates in general to an electrical capacitor which has a generally rectangular cross-section which is mounted so that it is centered in a housing which is in the form of a plastic cup having a rectangular cross-section and wherein said housing is provided with an opening through which power leads extend and the capacitor leads are attached to the plastic cup with a material which hardens.
The invention is also directed to methods for manufacturing such electrical capacitor in which the capacitor is inserted into a pre-fab plastic cup having a rectangular cross-section and the openings between the plastic cup and the capacitor are filled with a liquid hardenable casting material which subsequently hardens.
2. Description of the Prior Art
Capacitors mounted within a cup are known for example German Utility Model No. 6753341 discloses an electrolytic capacitor comprising foil windings mounted in a metal cup which has a round cross-section. The metal cup serves not only as protection for the foil winding, but also as one electrode of the capacitor. So as to attach the cup to the winding, the cup is provided with impressions at its internal surface and/or on its floor surface. These impressions are intended to prevent the cup from detaching from the winding during vibrations such as, for example, that occur in motor vehicles or during use of the apparatus in other environments and which could cause the connections of the one winding electrode to be detached from the cup due to vibration.
German Utility Model No. 19 26 788 discloses an electrical capacitor which has a cylindrical metal housing which has a beadlike projection approximately in the middle of the housing. The beadlike projection is intended to allow two small face spaces which are formed as a result of the projection to be filled with casting resin such that the one part is first filled with casting resin and after it is hardened, the second part of the housing is filled with casting resin. A corresponding capacitor is also disclosed in British Pat. No. 1,071,820.
German Pat. No. 1,299,073 discloses a method for integrating an electrical capacitor having end face contact surfaces in a cup-like housing. In the method disclosed, the electrical lead elements are first extended through the housing wall and are then connected to the face contact surfaces of the capacitor mounted outside of the housing and subsequently are inserted into the housing together with the capacitor. The disadvantage of this method is that the threading of the lead elements through the housing wall requires a considerable technical expense and is extremely susceptible to disruption of the method. Since the casting resin is very thin in the second casting, the holes provided for the lead elements in the housing wall must be dimensioned so that they are small since the casting resin would otherwise run out through such holes. For a fast threading of the leading elements through the holes, however, the holes should be formed as large as possible. The great possibility of disruptions in this method is a definite disadvantage.
German Utility Pat. No. 7,021,001 discloses a capacitor which has regularly attached leads in a prismatic shaped housing preferably composed of thermal plastic material. Upwardly projecting fork-shaped retaining clips are first injection molded to the housing and the retaining clips are bent by at least 90.degree. into the interior of the housing after the insertion of the capacitor and the leads are fixed with the forks. The purpose of the forks is to assure the maintainance of a precise grid dimension, in other words, of a defined spacing of the lead wires from each other. Fixing of the capacitor to the housing thus occurs only indirectly by way of the wires of the capacitor whereas centering of the capacitor inside the housing does not occur at all. Thus, it is disadvantageous in that the tabs which are bent into the cup require an inadmissible great integration space which cannot be used for the winding. Also, the elasticity required for the bending restricts the material selection so that cost beneficial material such as plastic cannot be used.
German Utility Model No. 19 11 606 discloses a rectangular plastic cup for capacitor windings which have parallel leads that extend out through sealing compound so as to prevent moisture from entering the cup. On the inside of opposite walls of the cup there are flexible longitudinal ribs so as to assure that the winding in a cup is surrounded by an adequately thick layer of a casting resin on all sides so as to achieve adequate moisture protection. The disadvantage of these longitudinal ribs is that first they can only be realized with difficulty using injection molding technology, for example, due to the required ejection of the part and second only small tolerances between the component links and the inside links of the cup can be resiliently compensated. As a result of the elastic ribs, the same disadvantages as listed for German Utility Model No. 70 21 001 also occur.
U. S. Pat. No. 3,806,766 discloses an electrical component and method for manufacturing it wherein the components are introduced into a housing. The housing has recesses in which the leads of the electrical components are guided. As a consequence of the spring tension of the leads, the component is held until the casting resin solidifies which is supplied at a later time. Here again the fixing of the component occurs only indirectly by way of the leads whereas a direct fixing using lips or similar structures does not occur. However, a clamping by way of wires is only possible with an extremely small tolerance range of 0.1 mm and depending on the shape of the wire results in a loss of useable space.
European Pat. No. 0 062 167 discloses an electrical component which is mounted and centered in a housing. The electrical component is mounted in a cup which has a rectangular cross-section. The power leads of the component extend out of the opening of the cup in the same direction. The cup has at least two clips of the same material attached of one piece on opposite sides wherein the clips are bent over into the inside of the cup and hold the component in a clamped manner due to their resiliency and serve as centering and adjustment of the component during casting with casting material and hardening thereof. Although components contained in such cups have been placed on the market wherein about several millions of such parts have been utilized, it should be noted that the clips make the manufacturer of the cup more expensive and bending over the clips before the introduction of the capacitor increases the cost in that an additional manufacturing step is necessary and a large amount of the useable space is lost particularly wherein small grid dimensions such as, for example, type RM5 for the winding dimensions are available.
German published application No. 32 16 192 discloses an electrical component which can be mounted and centered and adjusted in a housing in the form of a cup which has a rectangular cross-section. The cup is provided with bulges on opposite sides which provide a clamping holding action of the component. This cup has the disadvantage in that so as to introduce a component such as a capacitor a spreader tool must be used which spreads the inwardly arced walls of the cup apart so that the component can be introduced.
Italian Pat. application 35 50A/82 which was published on 30th March 1984 discloses methods for anchoring capacitive elements. In this structure, a capacitive element is secured to a housing and liquid thermal plastic material at a temperature which is above its solidification point is introduced in a small amount such that it only partially fills the housing and the electrical component is then inserted into the housing and the capacitive element is secured to the housing when the material cools and due to the solidification of the potting material. This patent application also discloses that the capacitive element can be secured into the housing with clips which are attached to the housing which are bent over into the housing after the introduction of the capacitive element. The clips can be attached either to the narrow sides or to the broad sides of the housing.
This Italian patent application discloses that at least a subregion of the side walls should be plastically deformed toward the inside of the housing until they rest against the capacitive element. The deformation can be preceded by heating of the subregion which is to be deformed to a degree such that the subregion is plastically deformed. Such deformations can be symmetrically associated in pairs to power leads.
This Italian patent application also discloses that concave portions can be provided at the power leads and these concave portions extend beyond the end faces in the longitudinal direction or in the transverse direction with respect to the end faces of the capacitor and also by using additional recesses in the housing which provide latching of the concave portions of the power leads which result in firm seating of the capacitive element in the housing. There is a disadvantage due to this structure in that the tolerances are very small and the tolerances occuring between the cup, the winding, and the wire can be greater than the elasticity of the wire.
Each of the methods disclosed in the Italian Patent Application serves the purpose for fixing the capactive element precisely in a position in the cup in which it has been inserted into the cup. The centering thus also occurs indirectly in this structure in that the leads of the capacitive elements are fixed by exact guiding clamps. Bent wires thus result in an imprecise centering of the component. This error is preserved when subregions of the side walls of the housing are subsequently deformed until they press against the capacitive element.